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Abstract
The use of chemical dispersants for the handling of oil spills has had a brief but highly turbulent history. Despite extensive laboratory data and field application experience, their role in oil spill cleanup is still controversial. This paper reviews some of this past history as background in order to derive the pros and cons regarding their use. Opinions vary from an extreme of no use whatsoever to an acceptance of as the only practical technique to combat an oil spill under rough sea conditions. Improvements in the formulation of dispersants during the past several years are reviewed. These innovations involve modifications to improve effectiveness, application techniques and toxicological properties. A brief outline of the mechanisms of dispersing is presented to permit a better understanding of these formulation modifications and the manner in which said changes influence dispersant properties. The future outlook for dispersants, based on current and anticipated research in this field, is also discussed. This research involves biological as well as operational aspects of dispersants

Abstract
In order to fully appreciate the development trend for the “next generation” chemical dispersants for oil spills, the current status of this field is briefly reviewed. Recent applications illustrate the specific beneficial potential role of chemical dispersants in the oil spill control, as well as their limitation. The present mechanism of dispersing oil spills by the application of chemical dispersants is well understood and is the subject of many technical papers. While there is some variation in the relative performance and toxicity of the many commercially available products, they all require mixing after application. In instances wherein the dispersant has been marginally effective, inadequate mixing was usually the reason. Thus, mixing is the limiting step rather than application. The mixing of an oil spill by boat propellers, fire hoses, etc., is laborious and time consuming. However, dispersant may be readily applied to large areas by aerial application similar to “crop dusting.” In some instances, the oil spill may even become inaccessible for convenient mixing (e.g. under piers, shallow water). Hence, the elimination (or minimizing) of the mixing step would be a major improvement in the dispersion process. The “next generation” oil spill dispersants will require little or no mixing energy and will approach spontaneous emulsification. The mechanism of “self mixing” is outlined in this presentation. Performance data comparing this generic type of chemical dispersant with the more conventional systems commonly used illustrate the major differences. Another important aspect of this system is the resultant dispersed oil droplet size. The remaining concerns and other considerations requiring further study are discussed

Abstract
This paper reviews the development during the past two years of self-mixing chemical dispersants to minimize damage from oil spills. Some history regarding the acceptance (or lack thereof) of previous conventional dispersants requiring mixing energy is covered so that the progress manifested by the current self-mix dispersant approach can readily be appreciated. The utility of the self-mix dispersant system is based upon both the elimination of the laborious mixing requirement and the formation of submicron diameter size oil droplets. The role of droplet size in the behavior and movement of dispersed oil as well as the effect of droplet size on the toxicological and ecological impact of the dispersed oil, are significant aspects that are discussed. The planned research to determine the fate of dispersed oil under actual field conditions is outlined. This will permit a more accurate and objective assessment of the impact of dispersed oil on the marine environment than is now available from the extrapolation of laboratory bioassays. For example, the rapid dilution-dispersion of the oil into a large body of water is an important characteristic and advantage of the chemical dispersion process and is very much influenced by droplet size. However, in laboratory tests the concentration of the oil is maintained at a constant level during the test exposure, and little attention is directed towards the determination or control of the dispersed oil droplet size

Abstract
There is increased recognition that there is a role for chemical dispersants in minimizing damage from oil spills. The improved effectiveness afforded by the self-mix dispersant system has been demonstrated. In addition, several organizations are planning major field demonstrations of this type of dispersant system. In these experiments, the water column will be sampled in the environs of the dispersed oil in order to establish the rate of dilution of oil concentration. The resolution of this important aspect (i.e., the dilution and resultant toxicity of dispersed oil) will help place the various laboratory bioassays, wherein dilution of the dispersed oil concentration is not considered, in a more proper perspective. Conventional (mixing required) dispersants will continue to be used in the immediate future where mixing energy is conveniently available and the spill size is relatively small. Hardware (sprays, booms, mixing breaker boards, etc.) have been well-developed for boat applications. In this regard, some dispersants are now formulated as concentrates (High surface-active agent content) for greater oil-to-chemical treatment ratios, thereby permitting workboats to remain on station longer before having to replenish supplies

Abstract
There has been an increasing awareness of the utility of conventional chemical dispersants in general, and self-mix dispersants in particular as a stable means to minimize damage from oil spills. This paper will update the use of, and activity regarding the self-mix dispersant as noted in applications over the past two years. In addition, these aspects that are still little understood are discussed. Specifically, uniformly sized, dispersed oil droplets of approximately 1 micron diameter are formed by the diffusion action of self-mix chemical dispersants. The droplet size influences the dilution rate of the spilled oil in field applications, and data to support this are presented. The results of laboratory bioassays performed with these much smaller dispersed oil droplets, as opposed to larger droplets formed with mechanical mixing, can be misinterpreted since the increased rate of dilution afforded by smaller droplet size are not replicated. In addition to the vital dilution study results, this paper also presents evidence to clarify several popular misconceptions regarding chemical dispersants. For example, it is explained that the apparent synergistic effects between oil and dispersant do not indicate that chemical dispersants release toxic substances from the oil into the water. Data is also presented which shows that dispersants do not cause the oil to sink

Abstract
An overview of the mechanism of chemical dispersion is presented in order to put the subject in the proper perspective. The methodology and role of the surface active agent in the generation of finely dispersed oil droplets are reviewed. This discussion of the dispersing mechanism will help resolve some of the misconceptions that have persisted for the past 10 years, such as the dispersant acting to either sink or solubilize the oil droplets into the water column, or both. The incentives, concerns, and resultant present status of chemical dispersion are developed

Abstract
Currently, mechanical cleanup techniques are conventionallt utilized to restore oil contaminated shorelines, such as marshland, beaches, sea walls, etc. Such methods can cause severe environmental damage. The approach is also inefficient in that oil removed from a shore surface by water jets or similar techniques can readily redeposit on a neighboring surface. This paper reviews the shortcomings of the expensive mechanical cleanup methods and presents the overall mechanism and technique for restoration using chemical agents. Although the use of chemicals in intertidal zones has not been well accepted by some environmental and regulatory groups, there is limited documentation that use of these agents results in less environmental damage and more rapid and economical shoreline restoration than mechanical alternatives. In support of this argument, an actual instance wherein an extensive Tampa, Florida shoreline had been oiled by a spill from the S/S Delian Appolon and subsequently chemically restored, is described. Detailed biological sampling of the biota in the environs of the work area was conducted by Texas A&M University. Data from an oiled area, oiled and chemically cleaned area and a control (as is) area are supplied in the presentation. The implications and feasibility of simply allowing the oil to weather/biodegrade in areas where this would be permissible are discussed, as are the proper, as well as improper, applications of chemical agents for shoreline restoration

Abstract
The effectiveness of a particular chemical dispersant in usually determined by various laboratory tests. Such laboratory performance cannot always be replicated in the field. The physical and chemical aspects of the actually spilled oil influence dispersant performance in a manner that usually cannot be extrapolated from the laboratory tests. Some of the important parameters discussed in this paper are the geometry, viscosity, and lens effect of the slick and the type of crude oil. Very thin slicks are sometimes not truly dispersed but are collected into a multiplicity of surface lenses by the penetration of the relatively large dispersant droplet. Heavily weathered and very viscous oil can resist contact with the more fluid dispersant and dispersant “roll-off” can ensue. An oil slick wherein 90% of the oil can be located in 10% of the area could result in overtreating some areas and undertreating others. The composition of the crude oil and its emulsion-forming tendency influence dispersant effectiveness regardless of other physical properties such as viscosity. This influence is more extensively discussed because of the unique effect of the crude oil composition on dispersant effectiveness

Abstract
Previous research has shown that crude oils contain various amounts of indigenous surface active agents that stabilize water-in-oil emulsions. It is also known that crude oils stabilize such emulsions to different extents. One aspect of the study was to investigate the relationship between the emulsion forming tendency of the various crude oils and the level of performance of a chemical dispersant on the particular crude oil. The results of the extensive laboratory test program indicated that dispersant effectiveness is a function of both dispersant type and the specific crude oil. However, there is no apparent correlation between the degree of emulsion-forming tendency of the crude oil, which is a function of the indigenous surfactant content, and effectiveness. A "clean" hydrocarbon, tetradecane (C14) was also tested in order to evaluate the absence of any indigenous surfactants on performance. It was found that tetradecane exhibited a higher level of effectiveness compared to the crude oils for each of the dispersants tested. In essence, the indigenous surfactants in the crude oil, in every instance, reduce dispersant effectiveness but to an unpredictable level. This is probably due to the fact that these agents present in crude oil promote a water-in-oil emulsion. Since the chemical dispersant is formulated to produce an oil-in-water dispersion, the interference of these crude oil surfactants is apparent. Hence, tetradecane would be an ideal test oil since the degree of dispersion of tetradecane by a particular dispersant represents the maximum dispersion effectiveness for that product. In order to establish more definitively the role of the indigenous surfactants, this surfactant phase was successfully separated from nine crude oils representative of different emulsion forming tendencies. It was found that the amount of surfactant residue extracted from the crude oil did correlate with the emulsion forming tendency of the crude oil. Finally, the above separated surfactant residue was added to tetradecane at the same concentrations as in the respective crude oil. As expected, in every instance, the surfactant residue decreased dispersant performance compared to "pure" tetradecane

Abstract
The following article discusses the relevance of laboratory toxicity studies of a chemical oil dispersant, in general, and the foregoing paper. While Lönning and Hagström use a sensitive means to determine the more subtle, sublethal effects of chemicals on marine life, two major aspects of their work should be clarified. First, a concentration of 1–10 ppm of chemical dispersant, wherein fertilization of the sea urchin egg was affected in their work, does not occur in the usual marine environment with proper use of the dispersant. Second, there is no evidence to support the conclusion that the specific chemical dispersants studied by Lönning and Hagström preferentially release ‘toxic substances’ from the crude oil

Abstract
The cleanup of oiled shorelines has generally been by mechanical, labor-intensive means. The use of surfactants to deterge and lift the oil from the surface results in more complete and more rapid cleaning. Not only is the cleaning process more efficient, but it can also be less environmentally damaging since there is potentially much less human intrusion and stress on the biological community because chemicals can make washing effective at lower temperatures. This paper will describe research on chemical beach cleaners for treatment of oiled shorelines that was initiated in support of the cleaning activities in Prince William Sound (PWS) following the Valdez oil spill in March 1989. The concept for using beach cleaners for shoreline cleanup is to apply a pre-soak to the weathered crude oil on shore and then flush with sea water to wash the oil into a boomed area for subsequent recovery. Criteria imposed on the use of chemical beach cleaners for the cleanup of the Valdez spill were: (1) effective rock cleaning agents should have very little or no toxicity to marine and terrestrial life, (2) there should be no dispersion of the oil washed from the shoreline into the water column; oil was to be recovered by techniques such as skimming or sorbents, and (3) the agents should be on the EPA National Contingency Plan (NCP) list. A laboratory scale rock washing test was developed to measure cleaner effectiveness and dispersion. A large number of commercially available formulated products were evaluated, as well as developmental formulations. The commercial products included all of the available NCP-listed products which could function as cleaners. None of the commercial products completely satisfied all the requirements established by the agencies for beach cleaning. However, a new formula, called Corexit 9580, consisting of two surfactants and a solvent was developed. It exhibited low fish toxicity, low dispersancy and effective rock cleaning capability. Although it was not approved for use in Alaska other than testing, subsequent work at Environment Canada confirmed the outstanding cleaning effectiveness and very low toxicity of the new product, and it is currently on the approved product list in Canada. The paper reviews the laboratory and field testing conducted to prove out this new product and highlights more recent work on mangroves to explore the potential use of Corexit 9580 to save and restore oiled vegetation

Abstract
Oil viscosity has been perceived as a major factor affecting the dispersibility of oil. Very high viscosity oils-20,000 centisokes (cs) or more-can readily be observed as resisting the breakup of the oil into dispersed droplets. However, there are instances where relatively viscous oil will disperse much more readily than another oil of similar viscosity. As extensive study has been conducted at ExxonMobil Research facilities in New Jersey to define the molecular makeup of 14 viscous heavy fuel oil products and to determine the property of the viscous oils, besides viscosity, that influences dispersibility. Dispersibility was measured by a standard laboratory dispersant test using a COREXIT dispersant selected from the U.S. Environmental Protection Agency (EPA) National Contingency Plan (NCP) product schedule. Initially, IATROSCAN (TLC) and gas chromatography data failed to show any correlation between chemical properties, such as sulfur, aromatics, paraffins, resins, vanadium, nickel content, etc. and dispersibility. However the analysis did identify a statistically significant relationship between a parameter based on normal paraffin content and dispersibility, which helps explain anomalies such as low viscosity oils that do not disperse. These results are expected to aid in guiding oil spill response for viscous oils

Abstract
An initial basic study focused on the interaction between dispersant surfactants and the oil-water interface. In essence, the study identified criteria to explain why a good dispersant is effective and why a poor dispersant is ineffective. The dynamic behavior of the oil-water interface, after the addition of the dispersant, was continuously monitored by a modified Wilhelmy plate device. This procedure provided much insight on the impact of the dispersant at the oil-water interface. One key finding of this study concerned the conditions for achieving very low interfacial tensions. It is known in microemulsion technology that a microemulsion formed by specific surfactants exhibits ultra-low interfacial tension against either oil or water. Microemulsion phase behavior studies then established that some specific surfactants, which form a certain type of microemulsion, are also highly effective dispersants, more effective than current stat-of-the-art products. This improvement results in the formation of much finer dispersed oil droplets generated by a very minimum and lower level of energy. This paper will review the results of the basic study and the subsequent formulation of an improved dispersant. Laboratory and field data evaluating and supporting the improved overall performance will be presented

Abstract
Using continuous flow bioassays, oil and oil/dispersant mixtures were used to contaminate food sources of larval American lobsters in order to determine lethal and sublethal effects of the pollutants on larval growth stages of the species. A 1:10 ratio of Corexit 9527/crude was used for these experiments. No additional toxicity was noted in oil/dispersant mixtures when compared to larvae exposed to a diet of crude oil-contaminated Artemia. Parameters included hydrocarbon content of water and tissues of larval lobsters, survival, molting rates, ammonia excretion rates, and O:N ratios

Abstract
As part of a multifaceted study to assess the impact of oil and oil dispersants on a model littoral ecosystem in the Baltic Sea, bioenergetic (O:N ratio) measurements were made for 2 of the predominant species, the mussel Mytilus edulis and the amphipod Gammarus salinus. In addition, ammonia excretion and respiration rate measurements for G. salinus and byssal thread production rates and spawning frequency observations for M. edulis were made. Four days after the start of the exposure, significant effects on byssal thread production rates and spawning frequency were observed for the oil/dispersant treatment. After 12 d the oil/dispersant group apparently had recovered whereas the oil-only group was exhibiting abnormal spawning behavior. No effects on ammonia excretion rates, respiration rates or O:N rates were observed after 1 d for G. salinus. After 10 d, however, highly significant differences were recorded between experimental groups and controls for all 3 parameters. While both oil and oil/dispersant treatments produced subtle physiological alterations in the animals investigated, the use of a chemical dispersant apparently resulted in a more rapid recovery of the species investigated than would have occurred if the oil had not been chemically dispersed

Abstract
Large-scale (4,500 L) exposure tanks supplied with a high-volume flow of seawater (3 turnovers/tank/day) were used to assess the effects of oil and oil dispersant exposures- and t assemblages of compatible marine organisms. The tanks were filled (15 cm deep) with clean, natural sediments and a natural benthic community to become established before the test animals were introduced into the tanks. The test animals used in this study included juvenile lobsters (Homarus americanus), bay scallops (Argopecten irradians), soft-shelled clams (Mya arenaria), and blue mussels (Mytilus edulis), all of which are commercially important species in New England. On August 8, 1984, 225 mL of light Arabian crude oil, equivalent to 50 mg/L oil added, were introduced into four of the six tanks. All the tanks were equipped with electric stirring devices and submersible electric water pumps to ensure adequate surface and vertical mixing. After 60 minutes, two of the oiled tanks received a 1:10 dispersant: oil spraying application of Corexit 9527. The mixing continued for six hours, during which time the seawater flow to the tanks was interrupted. After six hours, the seawater was restarted. Water, sediment flock, and tissue samples were analyzed for petroleum hydrocarbons by various techniques over the course of the three-month experiment. A number of physiological tests were performed with the experimental animals after the exposure to determine whether any subtle sublethal effects had occurred. These tests included bioenergetic, biochemical, and growth measurements. Seven days after the start of the experiment, the total hydrocarbon concentration was approximately twice as high in the mussels exposed to oil with dispersant as in those exposed only to oil, but this difference was less pronounced after three weeks. The aromatic compounds most persistently retained were the alkylated homologues of naphthalene, fluorine, phenanthrene. and dibenzothiophene, with the degree of accumulation roughly proportional to the degree of alkylation. For both oil and oil with dispersant groups, alkylated (C2 and C3) dibenzothiophenes were the compounds accumulated and retained to the greatest extent. No mortalities were observed as a result of the oil or oil with dispersant exposures. Highly significant differences were observed for Mya arenaria between the controls and both oil and oil with dispersant groups for condition index and shell growth measurements after two weeks. The condition index returned to control levels after four weeks, but the reduced shell growth rates persisted for the duration of the experiment. 0: N ratios for mussels and glycogen determinations of scallop adductor muscle and lobster digestive gland were significantly decreased at certain times for different treatments as compared with the controls. When sublethal effects were detected, they were usually observed for both oil and oil with dispersant treatments. From the results of this study we were unable to conclude that chemically dispersing the oil was more or less detrimental to the animals than physical dispersion alone. We believe that large-scale exposure systems are excellent models for evaluating the fate and sublethal effects of noxious agents on marine organisms

Abstract
Chemical dispersion promises to play an increasing role in the control of oil spills in the United States. The question of when and how dispersants are best used to protect the environment is the subject of considerable controversy. This controversy is generated, on one hand, by insufficient understanding of real-world dispersant effectiveness and environmental implications, and on the other, by lack of guidelines by which all relevant factors can be considered together. With time, the first aspect will ultimately be resolved. This paper presents an approach to the second. While a certain degree of pre-planning and preliminary decision-making can be accomplished, ultimate decisions to conduct chemical dispersions should be made on a case-by-case basis. Criteria for determining the acceptability of chemically treating a specific incident include human risk, feasibility and adequacy of physical control and recovery, dispersibility of the oil, logistic considerations, and whether dispersion will achieve a reduction in environmental impacts and interference with water usage. Assessed conservatively, these criteria should provide the basis for sound and acceptable decisionmaking. As knowledge in the use of dispersants improves, the validity of decisions using these criteria is expected to improve

Abstract
Experiments were undertaken involving laboratory studies in a small turbulent oil plume, investigations using revolving flasks, and in a small field test using a combined gas/oil plume. Tests revealed that emulsion is formed in plume from underwater blowouts, but that the formation of emulsion was averted by the presence of small amounts of demulsifiers or dispersants (250 ppm). Larger concentrations of dispersants broke up the oil, which was transported to the upper water level in the plume

Abstract
Low concentrations of BP light diesel (0.05%) and the oil dispersant BP1100X (0.005%), either alone or in mixture, stimulated the growth rate, biomass yield, chlorophyll a level and photosynthesis of the estuarine green alga Chlorella salina CU-1, while the same concentrations slightly inhibited algal respiration. The increase in the level of chlorophyll a may be one of the factors leading to elevated photosynthesis. BP light diesel and BP1100X at higher concentrations, as well as the oil dispersants BP1100WD and Shell Oil Herder at all the tested concentrations, reduced growth, chlorophyll a level, photosynthesis, and respiration of the algal cells. The inhibitory action of BP light diesel and the oil dispersants was concentration-dependent. Although both algal photosynthesis and respiration were reduced by BP light diesel and the oil dispersants, the effect on respiration was less severe when compared with that on photosynthesis. Shell Oil Herder, either alone or in combination with BP light diesel, were most toxic among the three oil dispersants tested

Abstract
Chemical dispersants are used in oil spill response operations to enhance the dispersion of oil slicks at sea as small oil droplets in the water column. To assess the impacts of dispersant usage on oil spills, US EPA is developing a simulation model called the EPA Research Object- Oriented Oil Spill (ERO3S) model (http://www.epa.gov/athens/research/projects/eros/). Due to the complexity of chemical and physical interactions between spilled oil, dispersants and the sea, an empirical approach to the interaction between the dispersant and oil slick may provide a useful or practical approach for including dispersants in a model. The main objective of this research was to create a set of empirical data on three oils and two dispersants that has the potential for use as an input to the ERO3s model. These data are intended to give an indication of the amount of dispersal of these oils under certain environmental conditions. Recently, the US EPA developed an improved dispersant testing protocol, called the baffled flask test (BFT), which was a refinement of the swirling flask test. Use of this protocol was the basis of the experiments conducted in this study. The variations in the effectiveness of dispersants caused by changes in oil composition, dispersant type, and the environmentally related variables of temperature, oil weathering, and rotational speed of the BFT were studied. The three oils that were tested were South Louisiana Crude Oil, Alaska North Slope Crude, and Number 2 fuel oil. Two dispersants that scored effectiveness above 85% by the BFT were selected for this study. A factorial experimental design was conducted for each of the three oils for four factors: volatilization, dispersant type, temperature and flask speed. Each of the four factors were studied at three levels except for the dispersant factor where only two dispersants were considered. Statistical analysis of the experimental data were performed separately for the three oils. Analysis of variance was conducted to determine which factors, or set of factors, were related to the percent effectiveness. Empirical relationships between the amount of oil dispersed and the variables studied were developed

Abstract
A factorial experimental design was performed using the Baffled Flask test to determine which factors (temperature, oil type, oil weathering, dispersant type, and/or rotation speed) are related to dispersant effectiveness. Three light to medium oils were used in this experiment (Number 2 fuel oil, South Louisiana crude oil, and Prudhoe Bay crude oil). Data analysis suggests a two-way interaction between factors; for South Louisiana crude oil, temperature and mixing energy; for Prudhoe Bay crude, temperature, mixing energy, and weathering; and for Number 2 fuel oil, only temperature. Researchers developed empirical relationships between amount of oil dispersed and variables that were studied

Abstract
Three oils and two dispersants were used to examine the factors that influence dispersant effectiveness in the Baffled Flask test. Oils were tested at three weathering levels to better understand the interactions between salinity and factors such as temperature, oil weathering, and mixing energy. Salinity was important in determining the significance of temperature and mixing energy on the effectiveness of dispersants for nearly all oil/dispersant types

Abstract
In order to better understand the practice of dispersant use, a review has been undertaken of marine oil spills over a 10 year period (1995–2005), looking in particular at variations between different regions and oil-types. This viewpoint presents and analyses the review data and examines a range of dispersant use policies. The paper also discusses the need for a reasoned approach to dispersant use and introduces past cases and studies to highlight lessons learned over the past ten years, focusing on dispersant effectiveness and monitoring; toxicity and environmental effects; the use of dispersants in low salinity waters; response planning and future research needs

Abstract
The role of geographic and socioeconomic factors on the effects of oil pollution in South Africa is discussed. The sparse population and natural mechanisms provide little reason for alarm in the case of an oil spill at sea except for certain higher risk areas. Effects of previous spills are outlined, and governance policy with regard to dispersant usage is discussed

Abstract
Research undertaken by Exxon Production Research Co. demonstrated that fire monitors could be used effectively in dispersant application if proper nozzles, pressures, flow rates, dispersant metering, and vessel operation practices to achieve proper dosages were used. Two systems were recommended, one of which automatically monitored water flow and injected the correct amount of dispersant in real-time, independent of pressure in the water line

Abstract
Four microbial species, Pseudomonas aeruginosa (ATCC 9027), Rhodococcus erythropolis and two Acinetobacter strains, were used to discover the effects of Triton X-100 and Tween-80 on their ability to biodegrade octadecane. P. aeruginosa and R. erythropolis showed enhanced mineralization of octadecane in the presence of the surfactants. The Acinetobacter strains showed higher rates of degradation of octadecane in the absence of Triton X-100 and Tween-80

Abstract
Oil spills have a devastating effect on biologically rich coastal environments. This report investigates this problem, covering damage by oil to biological systems, the use of dispersants (toxicity and considerations for dispersant use), impact of oil and dispersants on coral reefs, impact of oil on seagrass beds and sandy beaches, impact of oil on mangroves (seedling survival and tolerance, regeneration, forest type vulnerability, and cleanup and recovery activities in mangroves), conclusions, and recommendations. The study concludes that coral reefs and seagrass beds may escape significant spill damage if pollution is not chronic and if dispersants are not used. Sandy and rocky shores may be severely impacted but recover quickly. Mangroves are the most vulnerable coastal ecosystem. Recommendations are that oil spill contingency plans must be prepared for all areas, and that the necessary equipment for the plans must be in place

Abstract
As part of efforts to develop standardized testing protocols under the Chemical Response to Oil Spills Environmental Research Forum (CROSERF) and apply the results to real-world scenarios, three types of oil and two dispersants were tested in both continuous and short-term spiked exposures using the early life-stages of several marine organisms. Test species included embryo-larval stages of Pacific oyster (Crassostrea gigas), two marine mysids (Holmesimysis costata and Mysidopsis bahia), and two marine fishes (turbot, Scophthalmus maximus and inland silverside, Menidia beryllina). Oils were physically dispersed in seawater by vortex mixing in a flask and chemically dispersed using the same approach with COREXIT® 9527 or COREXIT® 9500 applied in a 10:1 oil-to-dispersant ratio to generate maximum exposure concentrations. Continuous exposure tests followed standard testing protocols for 96-hour or 48-hour duration, according to demands of the test species. Spiked exposures reflect continuous dilution of water column concentrations (half-life ~107 minutes), as observed in the field when oil is dispersed into open waters. Results are reported as the acute LC50s. Tests oil included fresh and weathered Kuwait crude, fresh Forties crude, and a Medium Fuel Oil (MFO) mix. Exposure concentrations for oil tests were quantified using gas chromatography and expressed as the sum of the C10 to C36 components, or TPH(resolved). Dispersant exposure concentrations were verified by UV spectrophotometric analysis. Not all species were tested with each oil and dispersant. For dispersants tested individually, constant exposure LC50s ranged from 3 to 75 mg/L, with oyster the most sensitive and turbot the least sensitive species. Spiked exposure LC50s ranged from 14 to >1055 mg/L among all test species. Dispersants were up to 36 times less toxic under spiked exposure conditions compared to similar treatments under constant exposure conditions. For oils, LC50s based on TPH(resolved) are similar for both the physically and chemically dispersed oil, demonstrating that dispersant did not increase the toxicity of oils based on measured exposures. Under constant exposure conditions, test species are very similar in sensitivity to the oils, with most LC50s around 0.5 ppm TPH(resolved). Spiked exposures were 4 to 100 fold less toxic to these test organisms. The more environmentally realistic spiked exposures demonstrate that standard, continuous exposure test data overestimate the potential toxicity of dispersed oil. When laboratory toxicity data are used as part of a dispersant approval process for spill response, the decision should take into account whether exposure durations and sensitivity of test species are representative of conditions in the spill area

Abstract
Four bench-scale dispersant tests were used to evaluate three dispersants, Corexit 9500, Superdispersant 25 and Agma Superconcentrate DR 379 with an IFO (Intermediate Fuel Oil) 180 and an IFO 380. Dispersant effectiveness was assessed using the Swirling Flask Test (SFT) and Baffled Flask Test (BFT) developed by the U.S. Environmental Protection Agency (EPA), the Exxon Dispersant Effectiveness Test (EXDET) developed by ExxonMobil, and the Warren Spring Laboratory (WSL) test utilized in the United Kingdom. This study allows comparisons among the small-scale laboratory tests and provides a basis to compare dispersant effectiveness data with findings from at-sea field trials and wave basin studies conducted with the same dispersants and oils. No single dispersant performed with the highest effectiveness under all test methods, but the data demonstrate that viscous oils such as IFO 380s could be dispersed under the right conditions. The results show that laboratory tests with greater mixing energy yield the highest estimates of dispersant effectiveness